What is UML?

UML stands for Unified Modeling Language. This object-oriented system of notation has evolved from the work of
Grady Booch, James Rumbaugh, Ivar Jacobson, and the Rational Software Corporation. These renowned computer
scientists fused their respective technologies into a single, standardized model. Today, UML is accepted by the
Object Management Group (OMG) as the standard for modeling object oriented programs.

Types of UML Diagrams

UML defines nine types of diagrams: class (package), object, use case, sequence, collaboration, statechart, activity,
component, and deployment.

Class Diagrams
Class diagrams are the backbone of almost every object oriented method, including UML. They describe the static
structure of a system.

Package Diagrams
Package diagrams are a subset of class diagrams, but developers sometimes treat them as a separate technique.
Package diagrams organize elements of a system into related groups to minimize dependencies between packages.

Object Diagrams
Object diagrams describe the static structure of a system at a particular time. They can be used to test class diagrams
for accuracy.
Use Case Diagrams
Use case diagrams model the functionality of system using actors and use cases.

Sequence Diagrams
Sequence diagrams describe interactions among classes in terms of an exchange of messages over time.

Collaboration Diagrams
Collaboration diagrams represent interactions between objects as a series of sequenced messages. Collaboration
diagrams describe both the static structure and the dynamic behavior of a system.
Statechart Diagrams

Statechart diagrams describe the dynamic behavior of a system in response to external stimuli. Statechart diagrams
are especially useful in modeling reactive objects whose states are triggered by specific events.

Activity Diagrams
Activity diagrams illustrate the dynamic nature of a system by modeling the flow of control from activity to activity.
An activity represents an operation on some class in the system that results in a change in the state of the system.
Typically, activity diagrams are used to model workflow or business processes and internal operation.

Component Diagrams
Component diagrams describe the organization of physical software components, including source code, run-time
(binary) code, and executables.
Deployment Diagrams

Deployment diagrams depict the physical resources in a system, including nodes, components, and connections.

What is a UML Class Diagram?

Class diagrams are the backbone of almost every object-oriented method including UML. They describe the static
structure of a system.

Basic Class Diagram Symbols and Notations

Classes represent an abstraction of entities with common characteristics. Associations represent the
relationships between classes.
Illustrate classes with rectangles divided into compartments. Place the name of the class in the first
partition (centered, bolded, and capitalized), list the attributes in the second partition, and write operations
into the third.

Active Class
Active classes initiate and control the flow of activity, while passive classes store data and serve other classes.
Illustrate active classes with a thicker border.

Visibility

Use visibility markers to signify who can access the information contained within a class. Private visibility hides
information from anything outside the class partition. Public visibility allows all other classes to view the marked
information. Protected visibility allows child classes to access information they inherited from a parent class
Associations
Associations represent static relationships between classes. Place association names above, on, or below the
association line. Use a filled arrow to indicate the direction of the relationship. Place roles near the end of an
association. Roles represent the way the two classes see each other.
Note: It's uncommon to name both the association and the class roles.

Multiplicity (Cardinality)
Place multiplicity notations near the ends of an association. These symbols indicate the number of instances of one
class linked to one instance of the other class. For example, one company will have one or more employees, but each
employee works for one company only.

Constraint
Place constraints inside curly braces {}.

Simple Constraint
Composition and Aggregation
Composition is a special type of aggregation that denotes a strong ownership between Class A, the whole, and Class
B, its part. Illustrate composition with a filled diamond. Use a hollow diamond to represent a simple aggregation
relationship, in which the "whole" class plays a more important role than the "part" class, but the two classes are not
dependent on each other. The diamond end in both a composition and aggregation relationship points toward the
"whole" class or the aggregate.

Generalization
Generalization is another name for inheritance or an "is a" relationship. It refers to a relationship between two
classes where one class is a specialized version of another. For example, Honda is a type of car. So the class Honda
would have a generalization relationship with the class car.

In real life coding examples, the difference between inheritance and aggregation can be confusing. If you have an
aggregation relationship, the aggregate (the whole) can access only the PUBLIC functions of the part class. On the
other hand, inheritance allows the inheriting class to access both the PUBLIC and PROTECTED functions of the
superclass.

What is a UML Package Diagram?

Package diagrams organize the elements of a system into related groups to minimize dependencies among them.

Basic Package Diagram Symbols and Notations

Packages
Use a tabbed folder to illustrate packages. Write the name of the package on the tab or inside the folder. Similar to
classes, you can also list the attributes of a package.

Visibility
Visibility markers signify who can access the information contained within a package. Private visibility means that
the attribute or the operation is not accessible to anything outside the package. Public visibility allows an attribute or
an operation to be viewed by other packages. Protected visibility makes an attribute or operation visible to packages
that inherit it only.
Dependency
Dependency defines a relationship in which changes to one package will affect another package. Importing is a type
of dependency that grants one package access to the contents of another package.

What is a UML Object Diagram?

Object diagrams are also closely linked to class diagrams. Just as an object is an instance of a class, an object
diagram could be viewed as an instance of a class diagram. Object diagrams describe the static structure of a system
at a particular time and they are used to test the accuracy of class diagrams.

Basic Object Diagram Symbols and Notations

Object names
Each object is represented as a rectangle, which contains the name of the object and its class underlined and
separated by a colon.

Object attributes
As with classes, you can list object attributes in a separate compartment. However, unlike classes, object attributes
must have values assigned to them.

Active object
Objects that control action flow are called active objects. Illustrate these objects with a thicker border.

Multiplicity
You can illustrate multiple objects as one symbol if the attributes of the individual objects are not important.

Links
Links are instances of associations. You can draw a link using the lines used in class diagrams.
Self-linked
Objects that fulfill more than one role can be self-linked. For example, if Mark, an administrative assistant, also
fulfilled the role of a marketing assistant, and the two positions are linked, Mark's instance of the two classes will be
self-linked.

What is a UML Use Case Diagram?

Use case diagrams model the functionality of a system using actors and use cases. Use cases are services or
functions provided by the system to its users.

Basic Use Case Diagram Symbols and Notations

System
Draw your system's boundaries using a rectangle that contains use cases. Place actors outside the system's
boundaries.

Use Case
Draw use cases using ovals. Label with ovals with verbs that represent the system's functions.

Actors
Actors are the users of a system. When one system is the actor of another system, label the actor system with the
actor stereotype.

Relationships
Illustrate relationships between an actor and a use case with a simple line. For relationships among use cases, use
arrows labeled either "uses" or "extends." A "uses" relationship indicates that one use case is needed by another in
order to perform a task. An "extends" relationship indicates alternative options under a certain use case.
What is a UML Sequence Diagram?
Sequence diagrams describe interactions among classes in terms of an exchange of messages over time.

Basic Sequence Diagram Symbols and Notations

Class roles
Class roles describe the way an object will behave in context. Use the UML object symbol to illustrate class roles,
but don't list object attributes.

Activation
Activation boxes represent the time an object needs to complete a task.

Messages
Messages are arrows that represent communication between objects. Use half-arrowed lines to represent
asynchronous messages. Asynchronous messages are sent from an object that will not wait for a response from the
receiver before continuing its tasks.

Various message types for Sequence and Collaboration diagrams

Lifelines
Lifelines are vertical dashed lines that indicate the object's presence over time.

Destroying Objects
Objects can be terminated early using an arrow labeled "<< destroy >>" that points to an X.
Loops
A repetition or loop within a sequence diagram is depicted as a rectangle. Place the condition for exiting the loop at
the bottom left corner in square brackets [ ].

What is a UML Collaboration Diagram?

A collaboration diagram describes interactions among objects in terms of sequenced messages. Collaboration
diagrams represent a combination of information taken from class, sequence, and use case diagrams describing both
the static structure and dynamic behavior of a system.

Basic Collaboration Diagram Symbols and Notations

Class roles
Class roles describe how objects behave. Use the UML object symbol to illustrate class roles, but don't list object
attributes.

Association roles
Association roles describe how an association will behave given a particular situation. You can draw association
roles using simple lines labeled with stereotypes.

Messages
Unlike sequence diagrams, collaboration diagrams do not have an explicit way to denote time and instead number
messages in order of execution. Sequence numbering can become nested using the Dewey decimal system. For
example, nested messages under the first message are labeled 1.1, 1.2, 1.3, and so on. The a condition for a message
is usually placed in square brackets immediately following the sequence number. Use a * after the sequence number
to indicate a loop.
What is a UML Statechart Diagram?
A statechart diagram shows the behavior of classes in response to external stimuli. This diagram models the
dynamic flow of control from state to state within a system.

Basic Statechart Diagram Symbols and Notations

States
States represent situations during the life of an object. You can easily illustrate a state in SmartDraw by using a
rectangle with rounded corners.

Transition
A solid arrow represents the path between different states of an object. Label the transition with the event that
triggered it and the action that results from it.

Initial State
A filled circle followed by an arrow represents the object's initial state.

Final State
An arrow pointing to a filled circle nested inside another circle represents the object's final state.

Synchronization and Splitting of Control

A short heavy bar with two transitions entering it represents a synchronization of control. A short heavy bar with
two transitions leaving it represents a splitting of control that creates multiple states.

What is a UML Activity Diagram?

An activity diagram illustrates the dynamic nature of a system by modeling the flow of control from activity to
activity. An activity represents an operation on some class in the system that results in a change in the state of the
system. Typically, activity diagrams are used to model workflow or business processes and internal operation.
Because an activity diagram is a special kind of statechart diagram, it uses some of the same modeling conventions.

Basic Activity Diagram Symbols and Notations

Action states
Action states represent the noninterruptible actions of objects. You can draw an action state in SmartDraw using a
rectangle with rounded corners.

Action Flow
Action flow arrows illustrate the relationships among action states.
Object Flow
Object flow refers to the creation and modification of objects by activities. An object flow arrow from an action to
an object means that the action creates or influences the object. An object flow arrow from an object to an action
indicates that the action state uses the object.

Initial State
A filled circle followed by an arrow represents the initial action state.

Final State
An arrow pointing to a filled circle nested inside another circle represents the final action state.

Branching
A diamond represents a decision with alternate paths. The outgoing alternates should be labeled with a condition or
guard expression. You can also label one of the paths "else."

Synchronization
A synchronization bar helps illustrate parallel transitions. Synchronization is also called forking and joining.

Swimlanes
Swimlanes group related activities into one column.

What is a UML Component Diagram?

A component diagram describes the organization of the physical components in a system.
Basic Component Diagram Symbols and Notations
Component
A component is a physical building block of the system. It is represented as a rectangle with tabs.

Interface
An interface describes a group of operations used or created by components.

Dependencies
Draw dependencies among components using dashed arrows.
Learn about line styles in SmartDraw.

What is a UML Deployment Diagram?

Deployment diagrams depict the physical resources in a system including nodes, components, and connections.

Basic Deployment Diagram Symbols and Notations

Component
A node is a physical resource that executes code components.

Association
Association refers to a physical connection between nodes, such as Ethernet.

Components and Nodes

Place components inside the node that deploys them.